Conventionally, light source devices that radiate a laser light to a casing of a light emission sealing body filled with light emission gas and use generated plasma are known (for example, refer to Patent Literatures 1 and 2). For example, in a light source device described in Patent Literature 1, feeding is performed between counter electrodes disposed in a casing made of glass to generate plasma by discharge between the electrodes and a laser light is continuously radiated to the plasma, so that a laser support light to be a plasma emission is put on/maintained. In addition, for example, in a light source device described in Patent Literature 2, a pulsed laser light is radiated to an electron emission metal disposed in a xenon lamp, so that a pulsed plasma emission is put on.